Narrow retained canvas stroke execution helpers

docs/modernization/roadmap.md

@@ -1,7 +1,7 @@
 # PanoPainter Modernization Roadmap
 
 Status: live
-Last updated: 2026-06-12
+Last updated: 2026-06-13
 
 This is the living roadmap for modernizing PanoPainter into independently
 testable C++23 components while retaining all existing functionality. Keep this
@@ -3083,6 +3083,15 @@ Results:
   execution helper wrapping `pp_paint_renderer`, while pad color selection,
   dirty-face iteration, framebuffer copies, quad upload, and draw execution
   remain retained.
+- `Canvas::stroke_draw` pad-pass dirty-face iteration, pad-region planning, and
+  NDC quad assembly now share a retained stroke execution helper callback
+  boundary, while Canvas still owns framebuffer copies, brush-shape uploads,
+  and draw execution.
+- `Canvas::stroke_commit` retained commit input texture/sampler binding,
+  erase/composite draw dispatch, committed-copy to the dilate scratch texture,
+  and dilate draw now share `legacy_canvas_stroke_commit_services.h`; history
+  readback, `ActionStroke` population, layer dirty-box mutation, and retained
+  RTT/framebuffer ownership remain in the legacy Canvas path.
 - `Canvas::stroke_draw_compute` frame planning now shares the retained stroke
   execution helper for brush-quad construction, mixer feedback bounds, 2D/3D
   projection selection intent, and frame assembly, while legacy projection